Performance Evolution and Application of Nox-SCR Catalyst on a HD Diesel Engine Using Ethanol as a Reductant

摘要

Nox –SCR based on Ag/ Al2O3 catalyst by using ethanol as a reductant has proven its ability to significantly reduce Nox emission in a simulated engine exhaust gas environment. However the real engine exhaust gas environment is too complicate to be simulated. So the research of the Ag/ Al2O3 catalyst for real diesel engine exhaust gas environment is necessary. In this work, firstly the catalyst performance was evaluated on an engine bench and the effect of the catalyst on PM emission was investigated. Then the aftertreatment system composed of Ag/Al2O3 catalyst + Cu/TiO2 catalyst + Pt/TiO2 catalyst and Ethanol dosing control based on open loop control was designed. Finally the diesel engine emission with the aftertreatment system was tested on the ESC test cycle. The result showed that under the condition of fresh catalyst and SV=30,000 h-1, high Nox conversion (up to 90%) can be obtained in the range of temperature 350~450 . The Nox conversion efficiency will go up °C with the increase of the ethanol dosage, but cause the great increase of the CO emission and THC emission at the same time. Under the condition of inlet temperature =400 °C and nE:nNOx=1.5, the Nox conversion can maintain above 70% when the space velocity is less then 50,000 h-1. The aging test showed that sulfur absorbed on catalyst surface is the main reason for catalyst activation decreasing. The Ag/ Al2O3 catalyst can effectively decrease the SOF in PM, but have no effect on dry soot (DS). The Ag/Al2O3 catalyst can decrease the sulfate slightly when temperature is below 410 , but dramatically increase °C the sulfate when the inlet temperature is at 470 °C. Totally, the PM emission can be decreased more than half of the original engine out under the condition of inlet temperature 336°C, but increased a little when inlet temperature is at 470°C. The engine emission based on the ESC test cycle showed that engine with the aftertreatment system can completely meet EURO regulations with a original Ⅲ Nox emission of 13.06 g/kw.h.